1. Field of the Invention
This invention relates to a method of forming a fine structure on a compound semiconductor and particularly relates to a method of forming a fine structure on a compound semiconductor with inclined ion beam etching.
2. Description of the Prior Art
Methods of forming a quantum fine structure by etching a semiconductor layer having a quantum well structure with an etching mask having a fine pattern is known. Dry etching is one of efficient methods for such methods because it provides a high controllability and a high aspect ratio.
In the optical devices, electronic devices, and optoelectronic integration circuits used in optical information processings, optical communication systems, or optical measurements, characteristics of devices can be improved by applying a fine-processed structure, such as a quantum wire or quantum box structures to an active layer of a semiconductor laser to obtain compactification and high functions of the device. The dry etching has a high controllability and can provide a high aspect ratio in the processing of forming a wire including a quantum well structure with an etching mask having a fine patten.
FIGS. 4A to 4D are cross-sectional views of a semiconductor material to be processed through a prior art processing method for illustrating processing of a prior art for forming GaAs quantum wires. The quantum wires 49 as fine structures are obtained as follows:
A silicon dioxide film 46 is formed as an etching mask by deposition of silicon dioxide on a wafer comprising: a GaAs buffer layer 42, Al.sub.0.3 Ga.sub.0.7 As barrier layer 43, GaAs/Al.sub.0.3 Ga.sub.0.7 As multiquantum well layer 44, and an Al.sub.0.3 Ga.sub.0.7 As barrier layer 45 are consecutively grown by crystal growth on a GaAs substrate 41. A resist pattern 47 is formed by the electron beam lithography or the like as shown in FIG. 4A.
The silicon dioxide film 46 is etched by an etchant including a hydrofluoric acid in order to transfer the pattern of the resist 47 thereon as shown in FIG. 4B.
The Al.sub.0.3 Ga.sub.0.7 As barrier layer 43 and the GaAs/Al.sub.0.3 Ga.sub.0.7 As multiquantum well layer 44 are consecutively etched by a chlorine plasma atmosphere 48 using the silicon dioxide film 46 as an etching mask as shown in FIG. 4C.
The etching is continued and then, GaAs/Al.sub.0.3 Ga.sub.0.7 As multiquantum wires 49 are formed. At last, the etching mask of the silicon dioxide film 46 is removed as shown in FIG. 4D.
However, it is difficult to make side wall surfaces of the GaAs/Al.sub.0.3 Ga.sub.0.7 As multiquantum wire 48 vertical by the processing using the dry etching mentioned above. Therefore, the GaAs/Al.sub.0.3 Ga.sub.0.7 As multiquantum wire 48 is formed to have a cross section with a trapezoid shape. Thus, there is a problem that a multiquantum wire with uniform width cannot be obtained. Uniformity of width of each of quantum wires directly affects characteristics of the device having the quantum wires. That is, it is difficult to obtain etching with a high density of wires per unit area and a high uniformity in width or space width of the wires per unit area though the dry etching providing a high aspect ratio is used.